1. Field of the Invention
The present invention relates to lens inspection systems, and more particularly, the invention relates to automated systems and methods for inspecting ophthalmic lenses by acquiring and analyzing a plurality of images of the lenses being inspected.
2. Description of Related Art
Precision and accuracy in manufacturing ophthalmic lenses, such as contact lenses, are crucial for the use of such lenses in patients. Due to the increased demand for contact lenses, the manufacturing process of contact lenses has been automated to reduce manufacturing time and increase product turnover. However, the contact lenses are susceptible to damage, abnormalities, or contamination that would make the lenses unsuitable for use in patients. Accordingly, it is desirable to provide an inspection process of the manufactured lenses to reduce, and preferably eliminate, production of defect lenses.
Examples of contact lens inspection systems are disclosed in U.S. Pat. Nos. 5,500,732; 5,574,554; 5,748,300; 5,818,573; and 5,828,446.
U.S. Pat. No. 5,574,554 discloses an automated contact lens inspection system that inspects a contact lens while the lens is still in place on a transparent lens mold. The system uses a white light source that emits collimated white light through the transparent lens mold and through the lens being inspected to a camera. The camera utilizes a lens having a viewing angle that is constant within 0.5° for a ⅔ inch CCD array camera and 0.4° for a ½ inch camera, which is important in that system for the optical detection of the edge of the contact lens. The camera acquires a single image of the contact lens and converts the image into a digital representation of the lens for further processing by a computer to detect abnormalities of the lens.
U.S. Pat. No. 5,818,573 discloses an ophthalmic lens inspection system that uses diffuse white light to illuminate an inspected lens. The lens inspection system utilizes a plurality of cameras to acquire images of the inspected lens, and each camera is provided with a light source. The cameras that image the lens edge only image a portion of the lens edge. Accordingly, in order to obtain a complete image of the ophthalmic lens edge, eight cameras perimetrically disposed around the ophthalmic lens are used. Each camera is positioned at an acute angle with respect to the plane of the lens support. Each image acquired by each of the eight cameras is separately processed to minimize computational processing power. The system of the '573 patent does not inspect lenses for defects, instead, the system of the '573 patent inspects lenses to determine whether the lens is properly centered on the inspection system.
U.S. Pat. No. 5,500,732 discloses an ophthalmic lens inspection system that utilizes non-infrared light to image a hydrated lens. The light must pass through a ground glass diffuser, an air spaced doublet collector lens, and a field lens. The numerous components required in the inspection system necessarily require precise alignment and spacing of the various optical components in order to achieve the intended results. The image processor acquires a single image from the camera and analyzes either the center of the ophthalmic lens or the edge of the ophthalmic lens.
U.S. Pat. Nos. 5,748,300 and 5,828,446 disclose an automated lens inspection system that inspects hydrated lenses using dark field illumination. The lenses are imaged in a single step thereby contributing to the continuous lens inspection cycle disclosed therein. Each dark field image of a lens may reveal the lens edge as well as any defects or abnormalities in the lens that are sufficient to cause a scattering of light so that the light is imaged by the camera.
The lens inspection systems disclosed hereinabove that acquire only a single image of the ophthalmic lenses are susceptible to high false rejection rates, which may be caused by debris within the system or on the lens, or which may be caused by “noise”, such as optical noise, within the system. For example, these systems are not readily able to determine whether a potential defect near the lens edge is actually a defect of the lens, or whether it is debris on the window on which the lens is positioned. Accordingly, these systems may have high false rejection rates (e.g., rejection of lenses that were placed on a contaminated window), or may accept lenses that have small, but significant, defects near the lens edge.